Motor control.



UNITED STATES PATENT onnron- ERNST F. W. ALEXANDERSON, OF SCHENEC-TADY,NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEWYORK.

MOTOR GONTROL.

Specification of Letters Patent.

Patented April 21, 1908.

Application filed January 26, 1907. Serial No. 354,269.

To all whom it may concern:

Be it known that 1,-ERNsr F. W. ALEXAN- DERSON, a subject of the King ofSweden, residing at Schenectady, county of Schenec tady,-St-ate of NewYork, have invented certain new and useful Im rovements in MotorControl, of which the following is a specifica- 121011.

My invention relates to the control of commutator motors, which aredesigned to be operated as series motors on direct-current and'asrepulsion motors on alternatingcurrent, and its object is to providea novel control system forsuch'motors possessing a number of advantaeous features.

It is frequent] r esirable to operate commutator motors 0th on directand alternating-currentas, for instance, in the case of a r'ailway whichis operated ever part of its length on direct-current, and over anotherpart of its length on alternating-current. If

. the motors are operated as series motors on both direct andalternating-current, the a-l' ternating-voltage supplied to the .motorsmust ordinarily be lower than it is permissible to use when the motorsare 0 crating on direct-current, because the difficu ties of commutationare greater in alternating-current operation. Consequently, the motorleads and connecting wires mustbe larger than would be required fordirect-current operation alone. By operating the motors as repulsionmotors for al'ternating current opera-' tion, the alternating-voltagemay be increased and the alternating-current .decreased as much asdesired, since the motor armatures -are shortcircuited, and nocommutation difficulties arise dueto the increase in voltage. But if thealternating-Volta e is made greater than the voltage employe fordirect-current operation, the strain on the motor insulation, Withcontrol systems -heretofore employed, will be intreased.

One of the features of my invention-con sists in so arranging thecontrol system that the alternating-current voltage may be made twicethat of the direct-current, without increasing the strain on theinsulation of the motors I accomplish this result bygrounding a pointbetween the terminals of the transformer winding which acts as thesource of alternating-current for motors, so that by connecting theterminals of the motor circuit to points on the transformerwinding onopposite sides of the grounded point the.

total voltage impressed on the motor circuit may be twice that existingbetween any motor winding and ground. Consequently, although thealternating-voltage may be twice that of the direct'voltage, the insulation strain is not increased. This feature of my invention is notnecessarily limited to motors connected as repulsion motors foralternating-current operation.

When a motor is to be operated as a series motor on direct-current andas a repulsion motor on alternatin -current, it is ordinarily desirabletodivide t e field winding into two portions, one of which is arrangedwith its axis at right-angles to the line of armature magnetization,serves as the exciting or field Winding for both operations, While theother, which has its axis parallel to the line of magnetization of thearmature, serves as a compensating winding for direct-current operation,and as the inducing winding for alternating-current operation. If thesetwo field windings, or portions of the field winding, are proportionedwith a relative number of turns adapted to produce the most satisfactoryoperation for the direct-current series connection, the proportions.will not be the best possible for t .e alternating-current repulsionmotor operation.

, One feature of my invention consists in increasing the eflectiveampere turns of the compensating or inducin winding relative td theexciting winding W en changing from the direct-current series connectionto the alternating current repulsion motor connec tion. If thealternating-current voltage were the same as, or less than thedirect-current voltage, this change in the relative numbers of ampereturns in the twowindings would preferably be made by decreasing thenumber of effective ampere turns of the exciting Winding when shiftingfrom directto alternating-current connections; but if thealternating-current voltage is greater than that of the direct-currentvoltage, the change is preferably made by increasing the effectiveampere turns ,of the compensating or inducing winding when changing fromdirect to alternating-current operation. In the control of more thanone'motor I prefer to produce this result by connecting the compeneatingindings in parallel for direct-current operation, and in series foralternatihg-current operation. a

When \relativeampcre trains of the tion than are required forcompensating windings are varied by increasing the efiective ampereturns of the compensating or inducin winding, when changing from directto a ternating-current o eration, the efi'ective number of turns of -t einducing Winding for alternatin -current operation is increased relativeto t e armature ampere turns.'- Consequently, the armature current isincreased relative to the current flowin through the field windings ofthe motor. With the usual connections employed for repulsion-motoroperation, this increase of the armature current would ne" turebrusheshas to carry only the difference between the armature current and thatin the field windings.

My invention will best be understood by reference to the accompanyingdrawings, in

which Figure 1 shows diagrammatically a control systemfor a pair ofcommutator motors arranged in accordance with my invention; Figs. 2 and3 show the circuit connections produced by the controlling switch of.Fig. 1, or direct and alternating-current operation, respectively; andFig. 4 shows a modification of Fig. 3.

In the drawings A A represent the armatures of two commutator motors.

B B represent the excitingor fieldlwindings-of the motors arrangedtoproduce magnetizations at right-angles to the magnetiza;

tion (produced by the armature current.-

represent windings having their axes in line with the lines ofmagnetization of the and serving as compensating windings fordirect-current operation, and

armatures,

as inducing windings for alternating-current operation.

D represents a commutating switch for connecting the motor for eitheralternating or direct-current operation.

E-represents a transformer servingas the source of alternating-current.The primary winding has one terminal connected through switch D to thetrolley, or other currentcollecting device, G, and its'otherterminalgrounded. The secondary of the transformer has its central pointgrounded,

- and means is provided for-connecting the motors to different points onthe transformer winding on oppositesides of thearound connection. Itwill be seen that wl'thithis ardevice G, and

.the armatures A and through the field or exciting vto ground. The fieldand armature windcircuit, but passes t rangement the voltage impressedon the motor circuit may be twice as great as the voltage existingbetween any motor winding and ground, or in other words, between anypart of the motor winding and the motor frame which is of course atground potential, so that the insulation straln on any motor windingwill not be greater than due to half the maximum voltage impressed onthe motor circuit. 7 V F represents a variable resistance forcontrolling the direct current voltage impressed on the motor circuit.

When the switch D is moved to bring the right hand movable contacts intoengage-' ment with the contact fingers, the circuit connections shown inFig. 2 are established. The current enters. through the collectingpasses through a variable portion of resistance F. It then divides,passing through the compensating windings C C in parallel. The currentthen passes through A 1n series, and windings B B ings of the two motorsare thus connected in series, while the compensating windings areconnected in arallel with each other, and in series with the otherwindings. This connection is that ordinarily employed for direct-currentseries motors, except that the compensating windings are in parallel.Owing to this parallel connection, the current throu half t at )assingthrough each motor armature. onsequently, the compensating windingsshould each possess approximately a little more than twice the effectivenumber of turns of each armature winding.

When the left-hand movable contacts of switch D, in F 1, are broughtinto contact with the contact fingers, the connections shown in Fig. 3are established. The primary winding of transformer E is con- I nectedbetween the collecting device G and ground, and. a connection isestablished from the movable secondary contact through the compensatingwindings C C in series, then through the armatures A and A in series,and through the field windings B and B in series to the lower secondaryterminal of transformer E. It will be seen that the armatures A and Aare short-circuited, but the connections of the armatures are such thatthe current passing through the compensating or inducing windings andthe field windings does not pass through the shortrough the motorarmatures. The relative directions of current at any. instant are asindicated by the arrowheadsfand since the inducing windings C are nowconnected inseries, instead of in parallel, and since eachinducing'winding h each compensating winding is one-' as twice theeffective turns of the corre- 'sponding armature, the armature currentmust be approximately twice the current in the inducing windings.Consequently, if '500 amperes are flowing through the inducing windings,approximately 1,000 amperes will be flowing through the armaturewindings. Of this, 500 will be flowing through the field windings, andthe 500 will be passing through resistances in circuit.

not shown a reversing switch, nor otherv the short-circuit connections,as shown by the arrow-heads. Consequently the short circuit connectionsneed carry only half the current flowing through the armatures. Itshould further be noted that the change in the connection of theinducing or comens'ating windings from parallel to series mcreases theireffective ampere turns with respect to the exciting windings foralternating-current operation. By this increase the best proportions ,ofampere turns of the two windings are secured for both direct andalternating-current o eration.

In Fig. 1 I have s own a two-coil transformer for supplying thealternating-current to the motors. If a single coil, or autotransformer,is employed, the same'result with res ect to the relative amounts of thetotal vo tage on themotor circuit and the voltage between the motorwindings and ground may be obtained by the arrangement.

of Fi 4, in which 'H re resents the auto transformer winding, w ich hasa point intermediate its terminals connected to r'ound. Except for thetransformer, this gure isthe same as Fig. 3, and requires no furtherexplanation. T

In order to simplify the drawin s as far as possible, I have merelyindicated diagrammatically switching means for controlling the amount oftransformer winding and Furthermore, I have details, which wouldordinarily be employed in the control system of a locomotive or car. All*the switches and the arrangement of the control ,system may be of anywell known type. Accordingly, I do'not desiretolimit myself to theparticular construction and arrangement of parts here shown, but aim inthe ap ended claims to cover all modifications W ich are within thescope of myinvention. r i What I claim as new and desire to secure byLetters Patent of the United, States, is,

1. In combination with a commutator motor, means for connecting saidmotor as a series-motor for operation on direct-current,- means forconnecting said motor as a repuls sion motor for operation onalternating current, a transformer winding adapted to sup.

' opposite sides of the grounded point.

' 2; In combination with a commutator mo tor, means for connecting thearmature in se current operation, and means for short-circuiting' thearmature for alternating-current operation Without breaking said serlesconnection, whereby the short-circuit connec tion carries only thedifference of the armature current and the current in other windings.

4. In combination with a commutator motor havmg an exciting winding anda compensating or inducing winding on its field structure, means forconnecting said windings in series with the armature for directcurrentoperation, and means for short-circuiting the armature foralternating-current operation and increasing the effective ampere turnsof the inducing winding relatively to the exciting winding.

5. In combination with a' commutator motor having an exciting windingand a compensating or inducing winding on its field structure, meansforconnecting said wind ings in series with the armature fordirectcurrentpperation, and means for short-circuiting the armature foralternating-current operation and increasing the eiiective ampere turnsof the inducing winding relatively to the exciting winding and to thearmature.

6. In combination with a commutator motor having an exciting winding anda compensating or inducing winding on its field ar-I mature, means forconnecting sald windings in series with the armature for direct-currentoperation, and means for increasing the effective ampere turns of theinducing-winding reiatively to'the exciting winding and to the armatureand for alternating-current operation and short-circuiting the armaturewithout breaking the series connection, whereby the-short-c1rcu1 t1 n,connection carnes .only

the difference of t e armature current and, the"current in the otherwindings; I

7 In combination with a pair. of commutajtormotorsieach having anexciting wind- -1ng and'a compensating or inducing winding on its fieldstructure, 'means for connecti the exciting windings and armatures ofbot motors in series with each other and connect-- ingf'the com ensatingwindings in parallel with each 0t er and in series with the otherwindings for (inset-current operation, and

means for connecting the compensating" windings ins'eries evith eachetherandshorttoo circuitin'g the armatures for alternating-current 0eration.

8. n combination with a motor adapted ing-current to said motor having apoint between its terminals grounded, means for establishing connectionsfrom the motor oireuit to points on said winding on opposite sides ofthe grounded point, and means for varying the voltage impressed on themotor circuit.

9. In combination with a motor adapted for operation on a1ternatin-current, a transformer winding adapted to supply alternating-current tosaid motor having a point between its terminals grounded, and means forestablishing connections from the motoroircuit to pointson said Windingon opposite sides of the grounded point and for varying the number oftransformer turns included between said points of connection.

In witness whereof, I have hereunto set my hand this 25th day ofJanuary, 1907. ERNST F, W. ALEXANDERSON. Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

